The development of high-power turbogenerators for the production of electricity has evolved with the aim of increasing unitary power, for a given ventilating gas, until reaching maximum dimensions and weight for handling, transport and installation of the turbogenerators.
Therefore, having established the type of ventilating gas and having reached the dimensional limits, increase in performance can be obtained by improving the ventilation methods and, therefore, cooling of the rotor electrical winding. A known ventilation method provides, in a ventilated rotor of a high-power turbogenerator for the production of electricity comprising a shaft extending along an axis, a plurality of axial slots obtained in the shaft, a plurality of conductor bars arranged at least partly in the slots, a plurality of axial channels suitable for ventilating the conductor bars and a plurality of subslots, for the ventilating gas to be distributed by the subslots to the axial channels and expelled from the latter at the level of the outer surface of the rotor.
The ventilated rotor of the type described has the drawback that, in order to increase the power of the turbogenerator, it is necessary to increase the dimensions of the rotor, for example the length, consequently lengthening the axial channels and increasing the temperature of the conductor bars.
In order not to exceed the temperatures established by the current regulations, increase in the length of the axial channels must be accompanied by an appropriate reduction in the losses per unit of length and, therefore, in the rotor current. This means that the specific power that can be delivered by the generator in terms of MVA/m3 (power of the generator/volume of active parts) decreases as the dimensions increase. In other words, the increase in power of the turbogenerator is not directly correlated with the increase in dimensions.